Rosalie Craig as Bobbie in the new production of Company at the Gielgud Theatre in London.
Photograph: Tristram Kenton for the Guardian

I am one of those people who generally dreads going to the theatre, mainly because I like to eat supper after 6pm but before 11pm. But I made an exception last week and went to director Marianne Elliott’s delightful new take on Company, Stephen Sondheim’s musical about single versus marital life. (I am also one of those people who loves Sondheim, and being someone who avoids the theatre but loves Sondheim is like loving to swim but hating the water. Welcome to my pain.)

In the original version, Bobby, a 35-year-old man in New York, frets about his perennially single status, while all his married friends urge him to commit. The first time I saw Company, I was a 33-year-old woman living in New York and as single as it was possible to be without being an actual nun, and, as much as I loved the musical, I left feeling furious. (Loving a musical and also feeling furious about it: truly, my pain never ends.) Was I really supposed to worry about a single 35-year-old man? I should probably mention here that I’d recently gone on a date with a single 35-year-old man who told me he normally only dated twentysomethings, but that for decrepit old me he’d made an exception. So forgive me, Sondheim, if my sympathy was in short supply.

Elliott has swapped the gender of the main character, turning Bobby into Bobbie, to make the show feel more modern. And it definitely helps. It also suggests that 35 is the new defining threshold for a woman.

“I never imagined I’d be single at 30,” I remember overhearing one of my teachers murmur to a colleague at school in the 1980s, and I took note: must be married by 30 (just one of the many lessons from school that failed to stick, along with trigonometry). Now that feels almost adorably young – although not as laughably so as 25. “Being a single 25-year-old woman was not an option back then,” Judy Blume told me when I interviewed her for this magazine and asked why, in the 1960s, she married the man who eventually became her ex-husband.

The day before I went to Company, it was confirmed that the actor formerly known as Meghan Markle, 37, is pregnant, and amid all the absurd hyperbole there were some wearily predictable digs. “There was always a faint worry about Meghan’s chances of conceiving naturally, as plenty of women her age do struggle,” tsked the Daily Mail. “Fertility falls off a cliff at 35, duchess or not.” Saucer of milk to table two, garçon!

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Some words about this fertility-destroying cliff, so famous it is probably a protected tourist site. Is it easier to get pregnant at 21 than 45? You will not be amazed to know that the answer is yes. But should a woman’s 35th birthday be a funeral for her fertility? Given how ubiquitous this theory is, you possibly will be amazed to learn the answer is no. As Jean M Twenge wrote in The Atlantic in 2013, this is based on a study that used French birth records from 1670 to 1830. Today, a woman in her late 30s has pretty much the same chances of conceiving naturally as a woman in her late 20s. And speaking as someone who got pregnant at Meghan’s age, I can confirm it is not just duchesses who manage this feat.

Yes, you have less time to get pregnant again if something goes wrong, and there is a slightly higher chance of miscarriage and complications. But this “35 or bust” narrative is toxic for young women, making them panic unnecessarily (as I did in my early 30s), and dangerous for older women, who think they can relax their contraception. (Several fortysomething friends have recently been shocked to find themselves booking an abortion.) Funnily enough, the risks for men delaying fatherhood – which are significant – are almost never mentioned. This is because the male narrative has many possible happy endings, whereas a woman without children is still seen as lacking.

Few things make the idea of a woman’s life having particular thresholds – married by this age! Babies by this age! – seem more absurd than crossing those thresholds yourself. Watching Bobbie’s friends in Company now, as a 40-year-old with a partner and children, the haranguing of single women that once felt so accusatory now looks ludicrous. What should a single 35-year-old woman do – get impregnated by a man she doesn’t really like, just in case? I can only assume the people who advocate this have never been in a relationship themselves, if they think that is in any way the safe option.

Biology may well impose some deadlines, but I have many female friends who – for various reasons – didn’t have children and are spending their 40s travelling the world, having exotic romances, scaling vertiginous career heights. There is nothing like looking through their Instagram feeds at 4am with a feverish toddler to make you wonder if the female storyline isn’t quite as narrow as you were told. A woman’s mid-30s is a time for decision-making, but we have more options than many realise. Love and fulfilment come in more shapes than a baby sling.